The goals of these studies are to better understand the mechanism and regulation of the synthesis and degradation of the nonessential amino acid proline. The strategy primarily involves delineation of naturally occuring and laboratory induced genetic defects in proline metabolism. By characterizing these mutant cell lines, we hope to learn more about both abnormal and normal proline metabolism. Mutant lines currently under investigation include two selected for resistance to the proline analogue azetidine carboxyl acid as well as several human lines lacking ornithine aminotransferase. We are also utilizing a cell line with high ornithine aminotransferase activity (10x other cell lines) to determine those factors which regulate the interconversion of proline and ornithine and thereby serve to replete or deplete the urea cycle of carbon skeletons.